Many methods for the precision transfer and handling of fluids are known and used in a variety of commercial and industrial applications. The presently burgeoning industries of the biotechnology and biopharmaceuticals are particularly relevant examples of industries requiring ultra-pure fluid handling and transfer techniques.
Various current fluid transfer methods require contacting the fluid with a transfer device, e.g., a pipette, a pin, or the like. Such contact methods dramatically increase the likelihood of contamination. Many biotechnology procedures, e.g., polymerase chain reaction (PCR), have a sensitivity that results in essentially a zero tolerance for contamination. Thus, non-contact methods for fluid transfer are desirable.
An exemplary non contact method for ejecting liquid droplets to a target location is described in U.S. application Ser. No. 09/735,709 filed Dec. 12, 2000 entitled “Acoustically Mediated Fluid Transfer Methods And Uses Thereof” and incorporated by reference in its entirety. This fine acoustic liquid ejection technique, however, may be improved by compensating for liquids having varying surface tension and viscosity values. It has been observed that such an acoustic liquid ejector can be limited or adversely affected by varying viscosity and surface tension values of the source liquid to be transferred. Indeed, volume and trajectory of droplet ejection depend upon the acoustic stimuli as well as the viscosity and surface tension of the liquid to be transferred. If the viscosity and surface tension are unknown, then the volume and trajectory of the transferred fluid may vary in an unknown manner. However, with knowledge of the viscosity and surface tension properties of each source, liquid, the acoustic stimuli used to transfer small amounts of fluid may be adjusted accordingly, improving the accuracy and precision of the transfer of that fluid. Thus, it would be advantageous to determine the viscosity and surface tension properties of each fluid prior to ejection. It is also desirable to determine this product in a manner that is easily automated.
Examples of conventional methods for measuring the viscosity of a fluid include capillary tube and rotary viscometers. These techniques require direct contact with the liquid to be measured which may introduce contamination when making multiple measurements.
Examples of conventional methods for measuring surface tension include: sessile drop, pendant drop, maximum bubble pressure, capillary height, the Du Noüy ring, and the Wilhelmy plate methods. All of these techniques have the disadvantage of requiring contact with the fluid or removal of a sample of the fluid.
Examples of non-contact methods of measuring surface tension of sea water are described in Can Cinbis, “Noncontact Techniques for Measuring Surface Tension of Fluids,” Doctoral Thesis, Stanford University, 1992. A first method involves measuring the water surface displacement caused by the radiation pressure associated with an acoustic pulse. The displacement is measured with a confocal optical microscope. The surface tension of the liquid is calculated from the measured values. The second method utilizes two ultrasonic transducers: the first transducer generates a wave and the second transducer measures the amplitude of the transient capillary wave a distance from the first transducer. The surface tension is calculated from the measured values. The technique, however, does not provide viscosity information.
None of the above described methods provide a non-contact method to measure viscosity and surface tension information as described herein.